The present invention relates to a method and a device for setting the longitudinal speed of a vehicle to a setpoint speed, in particular on the basis of a regulation, having controllable brake units.
The basic functioning of methods and devices for regulating the speed or acceleration is referred to as adaptive cruise control (ACC). A basic description of such a device and such a method can be found, for example, in the article xe2x80x9cAdaptive Cruise Controlsxe2x80x94System Aspects and Development Trendsxe2x80x9d by Winner, Witte et al., published at SAE 96, Feb. 26-29, 1996 in Detroit (SAE paper no. 961010).
Such a method and device are also described, for example, in German Published Patent Application No. 196 27 727, in which resuming regulation at an original setpoint speed is delayed by the driver in at least one operating mode. If, when regulation is resumed, the vehicle speed is greater than the stored setpoint speed, then, due to the time lag in resumption, the driver has an opportunity to adjust the setpoint speed to prevent an unwanted braking response.
German Published Patent Application No. 43 38 399 describes a method and a device that work together to regulate or limit driving speed. In this method, an estimate is made to determine whether a reduction in engine power will be sufficient to maintain a setpoint speed. If closing the throttle valve is not sufficient to decelerate the vehicle so that the setpoint speed is maintained, then, optionally, the braking power may be increased. This method is used to maintain driving speed at the setpoint speed, without having to operate the brakes by the brake pedal.
With conventional cruise control systems, in most cases only the throttle valve is controlled to regulate the actual speed of the vehicle at a setpoint speed. In isolated cases, there are conventional cruise control systems that can control the brake systems and can thus maintain a constant speed, even in downhill driving.
In vehicles with adaptive cruise control, both the throttle valve and the brake may be controlled, depending on the given situation. In an ACC system, this is done as a function of the speed or the distance from the vehicle in front, depending on whether the vehicle is in distance control mode or speed control mode. In the case when the vehicle is in speed control mode, i.e., no vehicle is within the sensor sight range in front, the setpoint speed is the same as the set speed selectable by the driver. In the case when the vehicle is in distance control mode, i.e., one""s own vehicle is following a vehicle in front, the driving speed approaches the setpoint speed. Therefore, in these ACC systems, braking may be performed automatically when the longitudinal speed of the vehicle is greater than the set speed. There are situations in which these regulating responses, in the form of braking measures, are undesirable and would frighten and even endanger both the driver and the following traffic.
This situation occurs in particular when the vehicle speed is significantly higher than the stored set speed, and the driver operates the resume button to reactivate the cruise control. Another situation in which this response can occur is when the driver steps on the gas pedal while ACC regulation is active and thus accelerates the vehicle to a significantly higher speed than the set speed. At the moment when the driver lets off the gas pedal again and the vehicle speed is still far above the set speed, the ACC regulation resumes and the vehicle is braked to the set speed, although the driver is not expecting this response.
The present invention may conform ACC control to the driving response of a skillful and experienced driver, so that in the situations described above, the system will respond differently than in normal operation. It is an object of the present invention to omit the control of brake units as long as there is no termination criterion, such as an obstacle detected in the predicted path range of the regulated vehicle or a time limit being exceeded, in particular in the special cases of resumption of cruise control and driver override in the case when the vehicle speed is higher than the set speed.
In an example method and device according to the present invention, the response of a natural driver in these special situations is simulated, thus avoiding unexpected and unnecessary braking maneuvers, which may frighten and endanger road users.